Lecture 2

Lecture 2, Wed 08/09

Python data and functions

Code from today’s lecture

Including the Turtle code

https://github.com/ucsb-cs8-m17/lecture2_0809

Questions and Answers

Q: Installing Python?
A: Visit http://python.org/download

lab00 and lab01

lab00 is now ready for you to work on it.
Eventually, we’ll explain how to work on labs on your own computer.
- If you want a head start on that, come to office hours with your laptop, and we’ll go over it with you.
For now, if you want to work on it before Friday, come to:
- Office hours in ~~Phelps~~ CSIL, today (Wed 08/09/2017, 3-~~5pm~~4:45pm) or
- Go to CSIL, Mon-Fri 8am-4:45pm
- The instructions for lab00 explain where CSIL is (ocean side of HFH)

Data Representation

int, float, str, list, tuple, dict

Functions

In Math: $f(x) = x^2$

In Python:

def f(x):
   " multiply x times itself "
   return x * x

return vs. print

I give you a dollar and you give me something tangible in return (that I can hold in my hand)

vs.

I give you a dollar and you “do something for me”

Economists call this a “good” vs. a “service”.

This is an analogy for return vs. print. We’ll explain more in lecture today and future lectures.

Turtle Graphics

We’ll use IDLE (for Python 3). The command to start it up at command line is idle3 (on CSIL, and on MacOS). (On Windows, look for IDLE in the Start Menu).

A few commands:

>>> import turtle
>>> fred = turtle.Turtle()
>>> fred.forward(100)
>>> fred.shape("turtle")
>>> 

Documentation for Turtle:

https://docs.python.org/3.6/library/turtle.html

Notes from IDLE on data represenation

Python 3.6.2 (v3.6.2:5fd33b5926, Jul 16 2017, 20:11:06) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "copyright", "credits" or "license()" for more information.
>>> print("Hello, World!")
Hello, World!
>>> 3 + 5
8
>>> x = 17
>>> x + 1
18
>>> x * 3
51
>>> x + 1
18
>>> x =  x + 1
>>> x
18
>>> x * 3
54
>>> 
====================== RESTART: /Users/pconrad/hello.py ======================
Hello, World!
>>> print ("Hello, World!")
Hello, World!
>>> 
====================== RESTART: /Users/pconrad/hello.py ======================
Hello, World!
>>> 
====================== RESTART: /Users/pconrad/hello.py ======================
Hello, World!
>>> 
====================== RESTART: /Users/pconrad/hello.py ======================
Hello,  World!
>>> 
=============================== RESTART: Shell ===============================
>>> ====================== RESTART: /Users/pconrad/hello.py ======================
SyntaxError: invalid syntax
>>> 
>>> 1
1
>>> 2+4
6
>>> -67
-67
>>> type(1)
<class 'int'>
>>> type(3 + 4)
<class 'int'>
>>> type(3.4)
<class 'float'>
>>> type("UCSB")
<class 'str'>
>>> schools = ["UCSB","UCLA","Stanford","Harvard"]
>>> schools
['UCSB', 'UCLA', 'Stanford', 'Harvard']
>>> len(schools)
4
>>> type(schools)
<class 'list'>
>>> type([23,5,7])
<class 'list'>
>>> type([2.3, -5.6, 17.0])
<class 'list'>
>>> stuff = ["foo",34,-8,True]
>>> stuff
['foo', 34, -8, True]
>>> len(stuff)
4
>>> type(stuff)
<class 'list'>
>>> stuff[0]
'foo'
>>> stuff[1]
34
>>> stuff[2]
-8
s
>>> stuff[3]
True
>>> type(stuff[0])
<class 'str'>
>>> type(stuff[1])
<class 'int'>
>>> type(stuff[2])
<class 'int'>
>>> for thing in stuff:
	print(type(thing))

	
<class 'str'>
<class 'int'>
<class 'int'>
<class 'bool'>
>>> for thing in stuff:
	print(thing,type(thing))

	
foo <class 'str'>
34 <class 'int'>
-8 <class 'int'>
True <class 'bool'>
>>> courses = ("CMPSC 8","MATH 3A","WRIT 2")
>>> len(courses)
3
>>> courses[0]
'CMPSC 8'
>>> courses[2]
'WRIT 2'
>>> type(courses)
<class 'tuple'>
>>> schools
['UCSB', 'UCLA', 'Stanford', 'Harvard']
>>> schools.append("Cal Poly")
>>> schools
['UCSB', 'UCLA', 'Stanford', 'Harvard', 'Cal Poly']
>>> schools.sort()
>>> schools
['Cal Poly', 'Harvard', 'Stanford', 'UCLA', 'UCSB']
>>> schools.reverse()
>>> schools
['UCSB', 'UCLA', 'Stanford', 'Harvard', 'Cal Poly']
>>> schools[-1]
'Cal Poly'
>>> schools[-1] = "Berkeley"
>>> schools
['UCSB', 'UCLA', 'Stanford', 'Harvard', 'Berkeley']
>>> courses
('CMPSC 8', 'MATH 3A', 'WRIT 2')
>>> courses.sort()
Traceback (most recent call last):
  File "<pyshell#57>", line 1, in <module>
    courses.sort()
AttributeError: 'tuple' object has no attribute 'sort'
>>> courses(-1)="MATH 3B"
SyntaxError: can't assign to function call
>>> courses[-1]
'WRIT 2'
>>> courses[-2]
'MATH 3A'
>>> courses
('CMPSC 8', 'MATH 3A', 'WRIT 2')
>>> courses[0]
'CMPSC 8'
>>> courses[-1] = "MATH 3B"
Traceback (most recent call last):
  File "<pyshell#63>", line 1, in <module>
    courses[-1] = "MATH 3B"
TypeError: 'tuple' object does not support item assignment
>>> schools[-1]="Princeton"
>>> schools
['UCSB', 'UCLA', 'Stanford', 'Harvard', 'Princeton']
>>> schools.pop()
'Princeton'
>>> schools
['UCSB', 'UCLA', 'Stanford', 'Harvard']
>>> schools.pop()
'Harvard'
>>> schools
['UCSB', 'UCLA', 'Stanford']
>>> schools.append("Yale")
>>> schools
['UCSB', 'UCLA', 'Stanford', 'Yale']
>>> englishToSpanish = { "one" : "uno", "two" : "dos" }
>>> englishToSpanish["one"]
'uno'
>>> englishToSpanish["two"]
'dos'
>>> englishToSpanish["three"]
Traceback (most recent call last):
  File "<pyshell#75>", line 1, in <module>
    englishToSpanish["three"]
KeyError: 'three'
>>> englishToSpanish["three"]="tres"
>>> englishToSpanish
{'one': 'uno', 'two': 'dos', 'three': 'tres'}
>>> englishToSpanish["four" : "cuaatro" }
SyntaxError: invalid syntax
>>> englishToSpanish["four" : "cuaatro" ]
Traceback (most recent call last):
  File "<pyshell#79>", line 1, in <module>
    englishToSpanish["four" : "cuaatro" ]
TypeError: unhashable type: 'slice'
>>> englishToSpanish["four"] = "cuaatro"
>>> englishToSpanish
{'one': 'uno', 'two': 'dos', 'three': 'tres', 'four': 'cuaatro'}
>>> englishToSpanish["four"] = "cuatro"
>>> englishToSpanish
{'one': 'uno', 'two': 'dos', 'three': 'tres', 'four': 'cuatro'}
>>> 